Cooperative Multiscale Aging in a Ferromagnet/Antiferromagnet Bilayer

TL;DR

This study investigates the aging dynamics in a ferromagnet/antiferromagnet bilayer using anisotropic magnetoresistance, revealing cooperative, power-law aging behavior with broad activation scales, akin to critical phenomena in complex systems.

Contribution

It demonstrates that aging in the bilayer is a cooperative process with power-law evolution, challenging simple models of independent subsystems.

Findings

Resistance exhibits power-law temporal evolution.

Aging involves a broad range of activation time scales.

Magnetic aging shows avalanche-like behavior similar to granular materials.

Abstract

We utilize anisotropic magnetoresistance to study temporal evolution of the magnetization state in epitaxial Ni$_{80}$Fe$_{20}$/Fe$_{50}$Mn$_{50}$ ferromagnet/antiferromagnet bilayers. The resistance exhibits power-law evolution over a wide range of temperatures and magnetic fields, indicating that aging is characterized by a wide range of activation time scales. We show that aging is a cooperative process, i.e. the magnetic system is not a superposition of weakly interacting subsystems characterized by simple Arrhenius activation. The observed effects are reminiscent of avalanches in granular materials, providing a conceptual link to a broad class of critical phenomena in other complex condensed matter systems.